My guess is that the rubber mounts on the pump are shot and that is contributing the the pump being louder than normal. Mounts are on their way so we'll give that a shot.

Ps. My brother has a '91 300D 2.5 Turbo and his pump doesn't activate like mine does upon start. When I have my hood open and I walk with the car as it rolls with my hand on the pump I can actually feel the pump activating for a second, with my brother's, I can't. Any insight into that irregularity?